1. Field of the Invention
The present invention relates to an apparatus for and a method of outputting an image, which are preferably applicable to a raster image processor, for use in a CTP (Computer To Plate) device or a CTC (Computer To Cylinder) device, for converting digital image data having values ranging from 0 to 255 into binary or four-valued digital image data based on which an image is recorded according to a scanning recording process.
2. Description of the Related Art
In printing and platemaking fields, it has heretofore been customary to produce printing plates for use on printing presses with a contact printer. In recent years, efforts are being made to carry out a printing process including the production of printing plates based on digital signal processing.
It is necessary in the art of printing and platemaking that the colors of a print sample and the colors (hues) of a print produced by a printing press be equal to each other.
In the conventional printing process of producing films from a platemaking process, producing printing plates from the films, and then producing a print from the printing plates on a printing press, if the colors of the print produced by the printing press do not agree with the colors of a print sample, then the operator first attempts to adjust the amounts of inks on the printing plates on the printing press which are usually a C (cyan) plate, an M (magenta) plate, a Y (yellow) plate, and a K (black) plate.
If the first attempt fails to achieve desired color matching, then the operator produces printing plates again to obtain adjusted hues. Specifically, films are placed in contact with printing plates in a contact printer, and the printing plates are exposed to ultraviolet rays through the films for certain exposure times. At this time, the exposure times are adjusted to change respective exposure levels of the C, M, Y, K plates for thereby changing gradations, so that the hues of the entire print can be adjusted. Heretofore, the exposure times are adjusted to change exposure levels (light intensities×times) in various stages, e.g., three stages, five stages, six stages, etc.
According to a recent new process which employs a CTP device with an ancillary raster image processor (hereinafter also referred to as “RIP”), the CTP device can produce exposed printing plates directly when it is supplied with digital image data having values ranging from 0 to 255.
However, the RIP associated with the CTP device does not have any means for easily changing the gradation characteristics of entire printing plates by changing exposure levels. In order to change the gradations of entire printing plates, it is necessary for the operator to go back to the process of producing digital image data to produce corrected digital image data.
Usually, the operator who works with the CTP device is often not skilled enough to produce digital image data on a workstation or the like, which is used to produce digital image data, and finds it time-consuming to produce corrected digital image data.
Another problem is that thanks to the advance of the network technology, the CTP device or a site where the CTP device is installed is often physically spaced apart from a site where digital image data is produced, so that it is actually difficult for the operator to go back to the process of producing digital image data to correct digital image data for changing overall gradations.
There has been proposed a technique for correcting gradations for the purpose of correcting the dot gain for printing in the RIP. According to the proposed technique, a printed material having patches representing overall gradations divided in 10 stages as a test chart, and the read values of halftone % of the patches on the test chart are supplied to the RIP to correct the dot gain thereof. However, such a process is considerably complex and time-consuming. While the proposed technique makes it possible for the operator to take time to adjust the RIP at the time the CTP device is installed, it cannot correct the hues of images readily in routine work.